Recently, a DNA micro-array is widely utilized in gene analyzing technology. The DNA micro-array comprises a support (i.e., micro-chip) of an extremely small area (such as approx. 1 mm2 or less) on which a group of nucleotide derivatives or their analogues (probes, e.g., DNA fragments, synthesized oligonucleotides or polynucleotide, PNA) are fixed. On one DNA micro-array, various kinds of nucleotide probes are fixed separately from each other.
In gene analyzing technology, detection of DNA fragments complementary to oligonucleotide probes whose base sequence is already known is very important.
The conventional procedure for detecting DNA fragments complementary to oligonucleotide probes are conducted in the following steps:                bringing single-stranded sample DNA fragments having a specific label (e.g., fluorescent label or radioactive label) in an aqueous solution into contact with a DNA micro-array having at least two defined areas in each of which a group of nucleotide derivatives and analogues thereof are fixed under such condition that a group of nucleotide derivatives and analogues thereof fixed in one area differs from a group of nucleotide derivatives and analogues thereof fixed in another area, so that DNA fragments complementary to a group of nucleotide derivatives and analogues thereof are fixed by hybridization to the area in which the group is fixed;        removing unfixed sample DNA fragments from the DNA micro-array; and        detecting the labeled DNA fragments fixed onto the DNA micro-array by hybridization utilizing an appropriate detection procedure.        
If a fluorescent label is employed, fluorometry is performed, while a radioactive label is employed, autoradiography is utilized.
The autoradiography utilizing a combination of a radiographic film and a radiographic intensifying screen is favorably employable as the detection procedure. However, since the amount of DNA fragments to be utilized in the detection is extremely small, the autoradiography sometimes shows unsatisfactory sensitivity.
Recently, a radiation image storing and reproducing method utilizing a radiation image storage panel (which is also named “stimulable phosphor sheet” has been widely employed in place of the conventional autoradiography, because the sensitivity provided by the radiation image storage panel is relatively high, as compared with the conventional autoradiographic system.
The use of the autoradiographic procedure utilizing the radiation image storage panel is already known. See Human Molecular Genetics, 1999, Vol. 8, No. 9, 1715-1722.
According to the studies performed by the present inventors, however, the high sensitivity of the radiation image storage panel sometimes shows analytical errors which are caused by the fact that the high sensitive radiation image storage panel absorbs not only the radiation energy emitted by the target DNA fragments (that is, the complementary DNA fragments but also radiation energy emitted by the non-target DNA fragments (that is, non-complementary DNA fragments) which are inadvertently fixed to the DNA micro-array not by hybridization.